One down, two to go. Reviews are in for the first of 2012's three big comic-book movies, Avengers Assemble, and the critics are doffing their caps to Joss Whedon's carefully curated, funny and grand ensemble superhero flick. Despite weighing in at a bum-numbing two hours and 23 minutes, the film already looks likely to be one of the best reviewed mainstream movies of the year, with a current 96% "fresh" rating on the critical aggregator site rottentomatoes.com.

Where previous Marvel studios films occasionally dipped from the high standard set by 2008's barnstorming Iron Man, Avengers Assemble manages to give all the main heroes and villains on show an acceptable amount of screen time. Whedon's Hulk, as played by newcomer Mark Ruffalo in both human and giant green rage monster modes (via motion captured CGI), quite simply smashes it. If the movie has a fault, it would be that the villains are a little insipid, and the denouement a tad by-the-numbers, but few critics are letting such misgivings bother them.

"As creatively variable and predictably formulaic as the Marvel films have been, this one will not only make the core geek audience feel like it's died and gone to Asgard but has so much going for it that many non-fans will be disarmed and charmed," writes the Hollywood Reporter's Todd McCarthy. "This is effects-driven, mass-appeal summer fare par excellence, that sought-after rare bird that hits all the quadrants, as marketing mavens like to say. As enormous as the production is, though, the appeal of the ensemble cast makes a crucial difference; you get enough but not too much of each of them, and they all get multiple scenes to themselves to shine."

"A beloved figure in the Comic-Con world, Whedon inherently seems to grasp just how much unbridled enjoyment there is in the prospect of uniting all these superheroes, and that enthusiasm pulsates throughout the film," writes Screen Daily's Tim Grierson. "Despite the occasional attempt at pathos, The Avengers isn't trying to replicate the moody drama of The Dark Knight. Rather, this film wants to put on a big, happy show, essentially asserting that while comic-book movies are serious business commercially, they also should be pretty fun. And this one certainly is."

"Joss Whedon's lavishly enjoyable, chewily titled film (the branding's there to warn British cinemagoers that John Steed will not be making an appearance) is an assemblage of everything that's good about contemporary popcorn cinema; just as importantly, it's a rejection of everything that isn't," says the Daily Telegraph's Robbie Collin. "Avengers might be short on bright ideas of its own, but co-writer and director Whedon has a magpie's eye for stealing other people's, and an enviable knack of improving them."

"Drawing together the meaty backstories of a half-dozen iconic heroes is no easy task – even with the help of the blockbuster Iron Man, Thor and Captain America movies that set up this showcase – but Whedon proves himself a master plate-spinner," writes my colleague Henry Barnes. "Each hero is given a convincing story arc, even if – as in the case of Jeremy Renner's Hawkeye – it's as shallow as revoking his lone wolf status to allow him to team up. Crucially, the wise-cracking id of Robert Downey Jnr's Iron Man is balanced out by instilling a hearty dose of fear in one of the team's central figures, thanks to a beautifully honed performance by Mark Ruffalo. He plays Bruce Banner – the brilliant scientist who turns into the uncontrollable colossus Hulk when angered – as a man afraid of himself."

Only one review out of 26 compiled by Rotten Tomatoes dares to give Avengers Assemble a bloody nose. Amy Nicholson of Box Office magazine feels Whedon's film lacks ambition and fails to flesh out its minor characters.

"The Avengers almost works. It's funny and it's physical, but even at two and a half hours, it plays like it's on fast-forward. Forget character development – there's not even character explanation," she complains. "The lesser Avengers are most slighted. After two movies with Black Widow and Hawkeye, I know less about them then I do the fighting Panda in Tekken.

"If such a thing can be said about a $220m dollar blockbuster, The Avengers needs more ambition. Sure, it's fine for most films to host their battle royale in downtown Manhattan, but the superfriends deserve more. Prehistoric metal monsters smashing up skyscrapers? We've seen that before."

With Christopher Nolan's The Dark Knight Rises and Marc Webb's The Amazing Spider-Man still to hit cinemas, it's looking like a definitive year for superhero movies. Avengers Assemble hits cinemas in the UK on 26 April, with the US following on 4 May. Are you unimpressed by all the hype, or already preparing to dive contentedly into comic-book bliss?